An admixture is a formulated composition other than a hydraulic cement (or binder), water and aggregates (such as sand and stones) that is used as an ingredient to control setting and early hardening, workability, or to provide additional cementing properties when making hardened binders (e.g., concrete, mortar, stucco or grout). Examples of binders, which are hydraulic cements, include Portland cement, or in combination with gypsum, aluminous cement and pozzolanic cement. Typically, an admixture is added to a batch of a binder immediately before or during mixing with water. Admixtures have generally been used to modify the properties of a binder so that it is more suitable for a particular purpose such as better handling characteristics during processing or for economic reasons. Generally admixtures are provided as single functionality additives that are added to improve a particular property of a hardened binder. Admixtures have been used to achieve certain structural improvements in hardened binders; improved quality of binders through the successive stages of mixing, transporting, applying and hardening of binders; improved processing characteristics especially in emergency situations during binder operations; and in cost reduction.
Admixtures have been available as water-soluble solids or powders that are mixed at the point of usage, or as ready-to-use liquids that are added at bulk blending locations. It has been desirable to provide pre-weighed quantities of admixtures so that the expected properties and performance of the binder batch are met. Small deviations from the recommended level of admixture to binder have been known to deteriorate the properties of the hardened binder, so it is desirable to have admixture compositions that are more forgiving in terms of admixture to binder ratio.
Pre-mixed blends of binder and admixture have been used. They require large quantities of the pre-mixed blends to be transported. It is preferable to be able to add a small quantity of an admixture to a commonly available binder, which is then hardened at a job site.
Even though there are a number of commercial powder and liquid admixtures, many of them have been based on lime-containing blends when used with binders. During handling the use of lime-containing blends has been deleterious to the health of workers. In addition, some lime-free admixtures have been found to provide inadequate weathering and strength properties to hardened binders, as well as inadequate handling characteristics during the processing of a mixture of admixture, binder, aggregates and water.
For the foregoing reasons, a need exists to provide improved lime-free admixture compositions for hydraulic cements and methods thereof. Such compositions must be safe and effective for use by workers and their method of use should preferably be easy to understand, routine and readily adopted. The inventor of this application has discovered admixture compositions and methods for hydraulic cements that meet these needs.